AU663137B2

AU663137B2 - Dual reflector offset active antenna

Info

Publication number: AU663137B2
Application number: AU30106/92A
Authority: AU
Inventors: Regis Lenormand
Original assignee: Alcatel NV
Current assignee: Alcatel Lucent NV
Priority date: 1991-12-23
Filing date: 1992-12-11
Publication date: 1995-09-28
Anticipated expiration: 2012-12-11
Also published as: DE69214412D1; EP0548876A1; AU3010692A; EP0548876B1; DE69214412T2; FR2685551A1; US5321413A; FR2685551B1

Description

6t3 1371 P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

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ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "DUAL REFLECTOR OFFSET ACTIVE ANTENNA" The following statemnent is a full description of this invention, including the best method of performing it known to us:..

Iy ;.i i: ?i ij i, i'ZZZvt This invention relates to a dual reflector offset active antenna, the two reflectors being in opposite positions with respect to their focal points according to a configuration of the "periscopic" type, well known under the English designation "offset fed Gregorian geometry".

An offset antenna of this type is particularly described in the article by Robert J.

Mailloux "Phased Array Theory and Technology" published in the American journal "Proceedings of the IEEE", Volume 70, No. 3, March 1982: see Figure 44(b), page 281, and its commentary and references on page 280.

As an indication, the enclosed Figure 1 shows, very schematically, the known configuration of a dual reflector active antenna of the offset type, which is the type of antenna concerned in the presei-, invention.

This antenna uses the principle of the optical periscope and it includes an active array 1, of small dimensions with respect to the direct radiation active array which would radiate according to a beam of diameter D identical to the beam finally radiated 15 by the dual reflector antenna with offset configuration.

This active array 1 is associated, in a typical way for this type of array, with S phase adjustment devices 2, and with amplifiers and filters (not shown), devices which will hereafter be referred to as "controls" in order to respect the terminology used by S those skilled in the art.

The beam of diameter which is radiated by the active array 1 is firstly S reflected by a first parabolic reflector 3, which focuses it on focal point F, and then, ortt from this focal point F, follows its path to illuminate a second parabolic reflector 4, opposite via its apex F to the reflector 3 and confocal to this latter, to finally radiate according to the beam of parallel rays of width D.

Note that in such a configuration, the transmitting source 1 is shifted with respect to the beam of width D finally radiated and that the antenna in question is thus an offset antenna as designated by those skilled in the art.

S o This configuration of the "periscopic" type with two reflectors 3, 4, is used for reducing the dimensions of the active source 1, and is a priori more advantageous than 30 the simple configuration which consists in having an active source of dimensions D j equal to those of the beam it transmits directly.

In fact, that the coirtraints imposed upon the components of the active source 1., of small dimensions are different from those imposed upon the equivalent active source of large dimensions which would directly radiate the beam of width D. It follows that, in reality, in order to obtain the same performances, one is constrained to reduce the ~i m dimensions of the components of the source 1, and finally to increase the number of adjustment devices, or "controls", associated with this source.

Finally, the economic balance and the bulkiness of a conventional antenna according to Figure 1 show that such an antenna, contrary to whatmay have been expected, does not bring any significant advantage with respect to the very simple antenna with direct radiation active array.

An object of the present invention is to offset this disadvantage.

According to the invention there is provided an offset-type active antenna having two reflectors, said antenna inciuding, at the focal points of the two reflectors, a radio lens one face of which, called "collector", receives and collects the focused beam reflected, from the beam transmitted by the active source of the antenna, by the first reflector encountered by the beam, the collector being placed at the focal point of the first reflector, and the opposite face of which, called "primary array", re-transmits towards the second reflector the energy transmitted to it via interconnections by said 15 collector, the primary array being placed at the focal point of the second reflector. The sources of the collector are respectively connected, one by one and respecting the same geometrical configuration, to those of the primary array, but said sources of the o° col!,;ctor each have much smaller dimensions than the sources of the primary array with Swhich they are associated. The co ',ction between each "small" source of the collector and the corresponding "large" source of the primary array includes a device for S finely adjusting the phase. This phase adjustment device is sampled on several distinct portions of said source of the primary array, which is thus in fact made up of an assembly of as many sources as portions.

der that the invention may be readily understood, embodiments thereof will 25 now b( scribed in relation to the accompanying drawings, in which: Figure 2 is a very simplified schematic diagram of the dual reflector offset active antenna, a diagram which is to be compared to that of Figure 1, described above, which represents the prior art; Figures 3 and 4 are respectively principle representations, given to facilitate the understanding of the invention, of the illuminated area of the colector and of the corresponding re-transmitting area on the primary array; Figure 5 is an electrical principle diagram of a possible mode of connection, with phase adjustment, between a "small" source of the collector and a corresponding "large" source of the primary array; and Figure 6 is a similar view to Figures 1 and 2, which shows a variant of 0 i implementation of an antenna according to the invention.

In Figure 2, the components identical to those of Figure 1 are indicated with the same reference numbers so as to facilitate the understanding and to avoid describing them again.

This antenna is different from that of Figure 1 in that it includes, at focal points F and F' of the two parabolic reflectors 3 and 4, an ultra frequency lens 5 which is composed of two interconnected arrays of sources: a first array of sources 6, called "collector", which is placed at the focal point of the reflector 3 and which receives the beam reflected and focused by the reflector 3.

The collector 6 is of relatively small dimensions, and (see Figure 3) is composed of a mosaic of a whole number n of "small" elementary sources 8, each of these receiving sources 8 being for instance made up of a small horn.

a second array of sources 7, called "primary array", which has much greater dimensions, in any case several times greater than the dimensions of the array 6, and which is placed at the focal point F' of the second reflector 4. This primary array 7 is placed on a surface parallel to that of the collector 6, and it is (see Figure 4) composed of a mosaic, homothetic to that of the collector 6, of the same whole number n of "large" unitary sources 9, each of these unitary re-transmitting sources being itself I t made up of a small mosaic of a whole number p (equal to 4 in the drawing) of small horns The "small" receiving sources 8 of the collector 6 correspond one by one, in a geographically homothetic way, with the "large" re-transmitting sources 9 of the primary array 7, that is to say the respective distributions of the sources 8 and 9 are the same-n each array 6 and 7. A source 8 of the collector is connected to the 25 geographically corresponding source 9 of the primary array via a connection which includes a device for finely adjusting phases, which will now be described with S reference to Figure In Figure 5, the "large" unitary 'purce 9 is assumed to be composed of a mosaic of four horns 10A, 10B, 10C and 1OD. This mosaic could obviously include another 30 whole number p of horns: six, eight, or even more.

The receiving horn 8, is connected to a divider by p (that is to say here by four), referenced 11.

The pjhere: folr) outputs 1PA to 12D of this divider 11 are linked to the portion of corresponding source 10A to 10D via'a respective adjustable phase shifter 13A to 130. Q I I I r ni~- ii? I t rt

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Thanks to these phase shifters 13A to 13D, a fine phase adjustment is performed on the signal re-transmitted by the "large" unitary source 9 towards the second reflector 4.

In fact, the primary array 7 is here positioned in the focal plane of focus F' of the reflector 4, while the collector 6 is placed in the focal plane of focus F of the reflector 3. In the case represented here, the collector 6 is close enough to the primary array 7 and, in first approximation, the two paraboloids 4 and 3 can here be practically considered as confocal.

One of the originalities of the invention thus consists in using sources of different diameters for the collector 6 and the primary array 7. The source-to-source connections of the collector and the primary array are such that in fact the sources of the primary array are excited with energy levels respectively approximately equal to the levels received by the corresponding sources of the collector.

The law of illumination of the second reflector 4 is the image of the distribution 15 collected by the sources of the collector 6. The transformation between the distribution radiated by the primary array is a function of the characteristics of the sources 8 of the collector and of the sources 9 of the primary array, given, of course, the fine phase adjustment introduced by the different phase shifters 13/ 13B, 13C, It should be noted that the connections according to Figure 5 are made sourceto-source and respect their rank in each of the arrays 6 and 7.

Figure 6 shows a variant of the antenna just described. According to this variant, the collector 6 and the primary array 7 are placed on surfaces which are no longer parallel at all, which is actually the case for the antenna of Figure 2. The lens 5 does not therefore have parallel faces.

25 This configuration has the advantage of allowing the dissociation of radici constraints from those of mechanical implantation of the components of the antenna.! The invention is obviously not limited to the example of implementation which has just been described. Although it is normally designed to be applied to satellite-borne antennas, its field is not so limited and it could just as easily be applied to ground antennas.

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Claims

1. An offset active antenna having first and second reflectors having corresponding first and second focal distances, a radio lens having a collector face at the first focal distance to collect a first focussed beam from the first reflector; the lens having a primary array at the second focal distance; the collector face including a first array of antenna elements each having a first cross-sectional area; the primary array including a second array of antenna elements each having a second cross-sectional area and each corresponding to an element of the first array; each element of the first array being connected to a corresponding element of the second array by corresponding connection means; Seach element of the second array occupying the same relative position c 15 with respect to the other elements of the second array as its corresponding i, element in the first array occupies relative to the other elements of the first array; the connection means including phiase adjusting means; P Oand wherein the second cross-sectional area is larger than the first cross- sectional area so that the primary array is larger than the collector. S

2. An antenna as claimed in claim 1, wherein the connection means include6s a divider to divide signals from each element of the first array into a group of two or more paths, each path including phase adjusting means, each group of paths being connected to the corresponding element of the second array. c 25

3. An antenna as claimed in any one of claims 1or 2, wherein the first array r is substantially parallel to a first plane and the secold array is substantially parallel to a second plane, and wherein the second plane is not parallel to the S ~first plane.

4. An active antenna substantially as herein described with reference to Figs. 2 to 6 of the accompanying drawings. DATED THIS TWENTY-EIGHTH DAY OF JUNE 1995 n ALCATEL N.V. -2 I: i I SUMMARY Offset-type active antenna having two reflectors 4) in periscopic configuration. A radio lens is provided at the focal points of the two reflectors 4). It is composed of a collector and of a primary array whose dimensions are much greater than those of'the collector. The "small" horn elements of the collector (6) correspond one by one, in a geographically identical way, to the "large" horn elements of the primary array to which they are respectively connected via fine phase adjustment devices. FIGURE 2. it itt 4 V IVVV I. V V t Vt I V Vt it V Vr S VVEV U o 44 i 1 i ii i iii i ~I